North Korea threatened a "miserable end" for South Korea's president and her American allies on Wednesday, in its latest colourfully worded attack.

Pyongyang declared it would wage a "retaliatory battle of justice" against Park Geun-Hye, with its artillery units standing ready to turn her office into a "sea of flames and ashes".

"What the DPRK warns is not hot air. It will be clearly proved by the miserable end the US and the Park group will meet while going reckless," said the Committee for the Peaceful Reunification of Korea (CPRK), using the formal name for North Korea.

The latest volley comes as Seoul and ally Washington stage their annual Key Resolve and Foal Eagle military drills, which this year are the largest ever, in the wake of a recent North Korean nuclear test and long-range rocket launch.

The massive drills -- which include air strike exercises targeting key facilities in the North -- are a "thrice-cursed provocation" against Pyongyang's leadership, the CPRK said, according to the KCNA news agency.

Seoul urged the North to stop "base and vulgar" threats and warned of a "relentless retaliation" against any future provocations.

"It would be a clear misjudgement on the North's side if the North believes that it can unnerve our government... with such ridiculous threats," Seoul's unification ministry, which handles cross-border affairs, said in a statement.

In recent weeks, Pyongyang has maintained a daily barrage of nuclear strike threats against both Seoul and Washington over the drills it sees as a provocative rehearsal for invasion.

Tensions have been running high since the North carried out an atomic test in January, followed by a long-range rocket launch that was widely seen as a disguised ballistic missile test.

The UN Security Council responded by slapping its toughest-ever sanctions on the North for violating UN sanctions that ban the isolated state from conducting any ballistic missile test.

In an apparent show of anger, the North has launched a series of short-range and medium-range missiles into the sea off its east coast since last week.

Cross-border ties are at their lowest in years, with the conservative Park maintaining her hardline stance towards the impoverished but nuclear-armed North.

She warned last week Pyongyang was moving on a path of "self-destruction" as leader Kim Jong-Un ordered a nuclear warhead test, in a move that further raised tension.